Various video signal processing systems using an auxiliary signal to augment a main signal are known. For example, the auxiliary signal may contain additional high frequency image information which for various reasons could not be included in the main video signal. The auxiliary signal also can include information useful for error correction and artifact compensation purposes.
An illustrative high definition television (HDTV) system employing an auxiliary second channel containing augmentation information is disclosed in U.S. Pat. No. 4,888,641 of M. A. Isnardi et al. The system disclosed in this patent is a two channel HDTV system wherein an auxiliary channel conveys information representing the difference between encoded extended definition image information conveyed by the main channel, and image information from an original source of higher definition image information.
It is desirable to digitally process high frequency information such as may be conveyed by an auxiliary signal for various reasons, such as to produce a better signal-to-noise characteristic. The use of such digital processing may involve data compression techniques which result in a variable data rate auxiliary digital signal. In such case special steps must be taken to assure that the main and auxiliary signals, which may exhibit different data rates, are properly synchronized when they are ultimately combined to reconstitute an image signal for display. The present invention addresses this consideration among others.